Rear Air Gap

[nymapleguy607]

I have a 2x6 raised flue and after test boiling this weekend I think I need to close up the air gap I left between the base stack and my down ramp. Currently I have it at about 10" from where my down ramp ends, to the base of the stack. and it is about 5" deep( from the top of the rail to the lower fire brick). So before I star to close this gap down I thought I would see what other people have there spacing at.
Thanks
Jeff

[Maplewalnut]

I have the same problem and plan on doing the same this weekend. the front of my flue pan boils like crazy. The boil decreases big time as you get closer to the stack.

[JohnsSugarShack]

I'm also in the same boat. Wasn't sure were to place the ramp. I was going to put it 12" from the stack but when I finished mortaring it in today I ended up with about 10" from the base stack to the top of the ramp.

[heus]

I ended up putting mine (2x6 deluxe Patrick Phaneuf) about 10-12" from the stack base. I was going to put it much closer, but Patrick told me to put it there so I did. During the test boil last night I had the same problem. A gusher of boiling sap in the front half of the flue pan and less in the back. less I'm going to leave it the way it is for this season since thats where he told me to put it. I can always change it next year.

[maple ridge tappers]

I have a 3'x8' small broths. lightning. The raised flue pan is 5'. The ramp ends at about 4' from the stack, but I have the arch beyond the ramp raised up with bricks to about 1" ( 1 inch, not foot) from the bottom of the flues. This way the draft forces the flames to travel through the flues and not just underneath them. Creates a vigorous boil throughout the flue pan, and greatly reduces fuel consumption.

[maple ridge tappers]

If you have a large area beneath the pan to close the gap between your arch and flues, and can't afford all the brick, a friend of mine used sand. It's a lot cheaper and creates the same affect.

[backyardsugarer]

I noticed the same thing on my test boil last night and will be using sand/brick to fill in the gap on my 2 X 8. Boiled hard in the front and first half the flue pan but near the stack just a simmer. I am going to fill right up to the baffle and leave 1" or so below the flues.

Chris

[nymapleguy607]

I have the space below my flues filled I have about 1" of space from the sand to the flues. The problem is how far away from the base stack do you start to taper your fill material down. When I asked the people at leader the said a 12" gap would be fine but I think I am going to knock it back to 6". I think this will help my syrup pan to boil harder and lower my stack temp some.
Thanks for the responses
Jeff

[flooder]

I guess I'm confused about the the air gap thing,do you have to worry about it with a drop flue arch?

[nymapleguy607]

No this is for a raised flue arch

[Amber Gold]

I have a simliar problem as you and I posted a similiar question on the "What's a 3x12 worth" There's an arch installation manual from D&G in there. Reading this I came to more questions. I down ramp currently starts 12-14" from the collar. I have stack temps in the 1400-1600 range w/ little boil in the back half of the flue pan. I think this is because there's too much exhaust area. Based on the area of my base stack, I'm going to reduce that to 8". I think with this reduction more heat will stay under the flue pan...possibly create more turbulance for better combustion of gases...not sure on the last part, just a thought.

[backyardsugarer]

do you cover your sand with bricks, add some cement or just put it in? I am concerned that with a blower it could move the sand around. I was going to cover the sand with bricks.

Chris

[nymapleguy607]

I only cover the backside of the sand with a couple of bricks I haven't had any problems with the sand blowing.

[Jeff E]

I use vermiculite insulation instead of sand. Sand holds moisture in the off season, is heavy and seams to speed up rusting out the arch.

Vermiculite is cheap, easy to work with, and insulates much better than sand.
I use it as filler, meaning the sides, ramp, and back area have brick.

[Ed K]

same problem,i thought of using lava rock to fill in space. I emailed the Proctor maple Center, they advised against this idea as the rock will take heat away starting up and lose it fast when your firing. So i have sand to put in same as you'all, i put a brick dam across at 5" from end of the flu pan so heat can pass to chimney.

[Bucket Head]

Guys,

I too have my bricks right up to the bottom of my flues at the rear. Just like the "brick dam" from one of the previous posts. However I have what you would think is an entirely too small a "gap" there. It is only a couple of inches in length by the width of the arch. I now have bubbles in the back of the pan where I had only a simmer going on there before.

You don't need a very large outlet for the "exhaust". I'll explain why. Think of your evap. as an engine. The exhaust valve is always smaller than the the intake valve. Why? Because the outgoing charge of spent fuel and air is just that- spent. It does not have the same volume as when it came into the cylinder before the spark plug ignited it.

Your incoming charge into your flue pan is superheated and "expanded". Hot anything expands and cold contracts, right? Your flue pan absorbs the "charge" leaving a lesser and cooler exhaust to exit. Whats going out can be considered spent. Your stack temp. is always less than what the firebox temp. is, right? The smaller "exit" opening allows the pan to absorb just a little more of the heat but still allows everything to exit.

You'll have to play with the bricks and see what works for you. I had to experiment too before hitting the set-up I've got now. It works great and I have not restricted the exit too much, meaning I don't have smoke and ash trying to blow out because I created too much back pressure.

By now, half of you guys are with me, and the other half are thinking "Wow, Bucket Head has hit his head a few too many times. He's really out there...". Thats allright. I'm telling you guys this so you can try it. It works and I would'nt tell anybody here that if it did'nt. Also remember, I've got pans made of 14ga. stainless. So if I've got bubbles at the back of my pan, I must have done something right! In a month or so, you can come see it for yourself if you want, I'll give you directions!

I will try to post a picture of the rear of my evap., but it might take a few days. Were going to be a little short on free time this week.

Steve

[backyardsugarer]

I put sand in yesturday and covered the top with fire bricks almost to the flue's. (1/2" gap) I left about a 4 inch gap in the back for exhaust that tappers down to the stack. I will find out how much difference it makes when I boil for the first time. No more testing.

Chris

[Toblerone]

I think you want to at least match the cross sectional area of your flue pipe. I have an 8" flue which would be 50 sq inches. Dividing that across a 2 foot arch would mean about a 2" minimum at the back of the pan. Unless, of course, you think your flue pipe is too big.

I think I'm running about 1" right now, I guess I should have done that math a week ago. But maybe I'm wrong. I guess I'll know in 2 weeks, if the weather cooperates.

[Maplewalnut]

My set up is currently vermiculite covered with ceramic blanket up to the rail. My down slope is now about 5 inches from the base stack opening. Not very gradual like it was when it was 12 inches away more of a hole instead of a slope. I'll let you know if I get better boil in the back. (no time soon, darn its cold out)

[Bucket Head]

Guy's,

The picture I promised of my rear air gap is the first pic in the modifications album on my photobucket link, thanks to my sisters boyfriend. Sorry for the delay. I should have taken the pic showing the entire flue pan brick arangment too, but I had the "gap" in mind and did not think of it.

You guys are going to say "no way can it work like that", but it does. Probably 90% of the raised flue arch's out there have too big of an area for the exhaust. Which allows too much heat to escape too quickly.

The bricks force the heat to exit the pan in the last inch and a half of each flue. Now I had to experiment with those last bricks and you will too. Each rig is different and a natural draft will require a larger opening than one with a blower. Also, the size of the blower and wether you have it blowing in "full" or restricted somehow (rheostat, diverters, intake blocked off, etc.) will affect the gap size.

Not everyone has one, but I could move those bricks back and forth through the flue brush door on the rear of the arch with a thin piece of rod with an "L" shape at the end for hooking the brick and pulling it back.

Like I said, it will take some time and trial, and possibly error(s), to get what works best. But with a little effort and almost no additional investment, you should be able to improve the efficiency of your arch/pan. I was able to and my pans are much thicker than most. They are 14ga. stainless.

So if you don't have much "action" going on at the rear of your pan, start thinking about how you can get that heat where it needs to be.

Steve

[Amber Gold]

Nice job on the evaporator. Why is your arch stepped up like that for the flue pan?

That looks tight. If I match the area of my 14" stack, I'm looking at a 6" gap from ramp to collar. I think my stack may be oversized though...I think newer 2.5x8's come with a smaller stack...maybe 12"

[Bucket Head]

Thank's Josh. I've put a great deal of time into making it what it is today. Its a lot different now then when I brought it home!

The arch had that step in it when I got it. I'm not sure what the builder was aiming for, but I kept it and ran with it from there. I am seriously considering air-over-fire modifications and if I do that I might modify the arch to a flat top design, although it would'nt need to be flat for the air-over to work. I was thinking that a flat top would be needed if I were to someday get a longer set of factory pans. However, my thoughts now center on an RO for more production, not another set of pans. But thats down the road a ways.

I could'nt tell you how my stack area relates to the performance, per say. My stack was a freebie, but it is also for a larger arch. I would have to do the math on the area to area figures. I'm sure my gap area is smaller than my stack area. Stack size and height is more crucial with a natural draft arch.

Steve

[markct]

ok so my 2x8 arch has 2 baffles of brick, one at the top of the slope which is about 12 inches from the front of the pan (6ft flue pan) this one is maybe 2 inches down from the bottom of the flues. the second baffle is about 10 inches from the stack and maybe 1 inch from the flues. the space between the two baffles is open, no vermiculite etc. am i losing alot of efficiency this way? my theory was that with the two baffles the heat had to go up thru the flue either way, so the open area in the center wasnt a big deal but maybe im wrong, i was thinking of closing up the back baffle to almost touching the bottom of the flues also

[Bucket Head]

Are you getting a good boil in the first two thirds of your pan? If so, then I'd say your alright with the bricks in the front. I would put the rear bricks up to the pan bottom with the smaller gap so your forcing all the heat to hit all the flues. That way you don't give the heat an opportunity to exit too early.

Steve

[Amber Gold]

From what I found last year, the open area in the middle is not a big deal. I have an access port in the back of my arch for cleaning the flues and I can see down the length of my arch. The flames stay inside the flues until they come to the end, where they drop down. I did notice my baffles had heat damage and warped, so I will be filling the area in w/ vermiculite to keep the heat off of them.

The flue pan is coming off this weekend and I will be re-bricking the back ramp next week

[markct]

Are you getting a good boil in the first two thirds of your pan? If so, then I'd say your alright with the bricks in the front. I would put the rear bricks up to the pan bottom with the smaller gap so your forcing all the heat to hit all the flues. That way you don't give the heat an opportunity to exit too early.

Steve

so would i maybe be better off to have just the bricks in the back? let the flames get up to the flues easier and just keep them from going out?

[Bucket Head]

It probably would work like that. I just don't have any experience with no front bricks at all up front.

The first thing I did to my evap. was to weld in a ramp going from the rear of the grate up to the flue pan about 8 inches back from the front of the flues. The bricks are up to the pan there. This way 100% of my heat/flame went into the flues and could not exit until it came to the gap.

This is where the experimentation comes in. Give it a try. If your boil is good now towards the front then change there might not be needed. If you like the idea of all your heat getting forced into the flues, get the bricks right up to the pan. There is a photo on Photobucket of my ramp and bricks at the front of my arch. Take a look at that for an idea.

Steve

[kinalfarm]

you can also just use mineral wool under the flu pan and set the flues right on it and it will push down so you know that you have no gap. thats what my wifes uncle does and at the end of the season he pulled it out and blow off hte ashes and it looks new. so you can tell that the fire hardly touches it, and hes got a blower so you know its real hot in there. he gets his hole flu pan rumbling real good.

[kinalfarm]

i would def. either insulate or brick up your ramp so that you have about 1'' gap under the flues so the flames and heat have to go through them. mine has about a 1/2'' gap and works good. i put mineral wool under the bricks to bump it up and re-bricked it

[markct]

well i slid the pan off today and put the bricks on the back baffle up so they almost touch the bottom of the flues, and its about 10 inches from the stack. the front baffle is about 2 inches down from the bottom of the flue pan, so maybe i will add that one another row of brick too, but then again maybe not, seems like it might be good to let the heat in but not out. so i gota wonder, if evap are supposed to be right up to the flues almost, why do they make them 8 to 10 inches deep in the back, why not about an inch more than the thickness of the insulation, and then step down for the stack?

[Bucket Head]

Thats a good question. I don't know why the factories have the large gap at the rear. Thats why I said most of the arch's out there are letting too much heat out too soon.

The only reason I can think of is that its a carry-over in design from back when there were no forced draft rigs, just natural draft, and the science of the day dictated a no-restriction draft.

Steve

[vtsnowedin]

The basic designs both dropped flue and raised flue were worked out back around WW1 by some very frugal Yankees without the aid of a wind tunnel or a CAD CAM program. They probably just moved the baffles back and forth until they couldn't see any improvement. My father told of running an older style rig on one side of the hill while my Grandfather ran a new king drop flue on the other with his three brothers gathering sap down first one side then the other. The King could make as much sugar in twelve hours as the old flat pan could in twenty four. Prices were high with the war already underway in Europe and they made enough to buy their first model T and pay cash for it. But with four single men and lots of dances to take the girls to it only lasted a year. The next spring my father was in France on his way up to the Grande Trenchee.

[Bucket Head]

Got any pics of either rig or the Model T?

Maple technology was pretty much the same old thing for decades and decades. Only recently has the technology advanced at a fast and steady pace. Think of what has changed in the last twenty or thirty years vs. the previous hundred years.

Steve

[vtsnowedin]

Got any pics of either rig or the Model T?

Maple technology was pretty much the same old thing for decades and decades. Only recently has the technology advanced at a fast and steady pace. Think of what has changed in the last twenty or thirty years vs. the previous hundred years.

Steve
No pics but I have the front to the King and the remains of both pans. The flat pan is galvanized and set under a haybarn for decades. The barn finally fell in one heavy snow year but the pan still rests up against a bit of the foundation wall. Up past the sugarhouse there is the remains of an old car but it's so far gone I can't tell what it is but most probably an A. Wrong farm anyway as the two sugarhouse setup was on Durgan hill in Vershire and I'm in Chelsea on what was a cousin's farm back before the war to end all wars.
That advance in technology in 1905 when Leader introduced the special was quite the revolution. Imagine a 100% improvement in production both per unit of time and unit of fuel. Thats what the fluepan rigs achieved over the industry standard of the day. You had to move forward or get out as those with new rigs could and would undercut your price. The year after they ran the two rigs at once they stopped using the old pan and started gathering the far side uphill and dumped into a dump station with a galvanized iron pipe to take the sap down to the new rig. They used both oxen and horses and some times the oxen were literally swimming through the snow as later when the snow melted you could see their frozen tracks with a foot of snow below them.

[Brent]

Someday we're all going to make some sense of evaporator design.

Half the members here seem to be putting a blower under their grates to blast air in under pans and up the stack and now on this thread we're talking about effectively choking the air flow to keep the heat under the back of the pans.

Hmmmm

Josh if you've got 1400 to 1600 degrees in your stack you're sending a lot of heat up the chimney. Hope you've got lots of wood.

Last year my local dealer who runs 3000 taps got a new Maxi-flu pan from Leader. He was thrilled to see his stack temps drop from just around 900 to about 850. Same burner, same GPH of oil, more boiling.

And the new Hurricane arch blows air in above the fire. I have no idea what the air gap is at the back near the stack. Sure seems like a lot of grist for the mill and gives us a lot to talk about here.

Meanwhile my wood guy dumped 3 cords on the front lawn today and its all got to be split down from "too big"
to "wrist size" so it will burn faster.

For what it's worth, my Phaneuf raised flue only boils vigorously in the front 12 - 16 inches. I filled under the flue pan with vermiculite and covered that with archboard, leaving about 1/4" to the bottom of the flues and a gap at the back about 4" x 24". Stack temps average 1050 - 1100. Near as I can tell goes through about 40 GPH and I think it's doing great. I just want more efficiency to cut down on the wood.

What would we call a small Hurricane?

[nymapleguy607]

I think we would call that a tropical depression.
I can tell can say I plan on closing up the back of my arch some. The current air gap is roughly 10". I think I am going to drop it to about 4"
that and I added a barometric damper in my stack. Will test it this weekend
and report back hopfully I can get the stack temp down to the 900 range
we will see.

[vtsnowedin]

Someday we're all going to make some sense of evaporator design.


What would we call a small Hurricane?
A Nor-easter?

[WESTVIRGINIAMAPLER]

This year at least for NE, it has been a Nor-leaster. LOL!

[Brent]

I've heard that Leader is working on an upgraded arch like the Hurricane

Someone also said that the techiniques that make the Hurricane so efficient are not easily done in a small rig.
I still have hope of getting better pressure jets above my fire this year.

[Bucket Head]

Brent,

I don't understand. How do you figure anyone is "choking their evaporator"? Please explain.

Steve

[Brent]

I have a 2x6 raised flue and after test boiling this weekend I think I need to close up the air gap I left between the base stack and my down ramp. Currently I have it at about 10" from where my down ramp ends, to the base of the stack. and it is about 5" deep( from the top of the rail to the lower fire brick). So before I star to close this gap down I thought I would see what other people have there spacing at.
Thanks
Jeff


Jeff says it here and the thread goes on about it. I'm not saying it's right, in fact I don't think the back end of the flue pan matters that much. If you've got a small clearance under the lenght of the flues, you've got almost all the hot air in contact with them and that's where the heat transfer happens. I don't think building a "heat dam" by moving the bricks closer to the stack and reducing the gap ( choking if you like ) will effect the heat transfer very much.

[vtsnowedin]

I have mine set back up the way it came from Grimm with the baffles set in thirds. A third of the flue pan over the ramp with the flames blazing right on them then a third filled in between the baffles to push the hot gasses up into the flues and a third for them to come back down and approach the stack entrance . If that does't work to suit me I can always add sand and bricks through the cleanout door but that might make cleanning the flues difficult.
When considering the thermodynamics of the smoke moving through the flues I think the gasses in closest contact with the top and sides of the flue get cooled rapidly and start to sink down the sides of the flue so that the hotter gasses in the center of the gap can rise up to touch the top of the flue. This sinking cooled gas would get to the bottom of the flues at some point and letting it continue to sink away from the flues lets the hotter gas have an unrestricted shot at the sheet metal. Perhaps the two thirds point is that point that has been found by trial and error. It is not a laminar flow of course but turbulent and much more complicated then I can discribe but I think that is one reason why the force five type arches use nozzles at angles to set up swirling and mixing patterns in the flow so that the maximum number of hot gas molecules come in direct contact with the pan metal before heading up the stack.

[Bucket Head]

Brent,

You would be surprised as to how much of a difference reducing the gap can make. Its not a "night and day" type of difference, but there is a difference. I now have boiling in areas of my flue pan that had no boiling before. That's a noticable difference in my opinion.

The opportunity for heat transfer is lost at the back when the heat and gases are allowed to exit the flues sooner than they need to. I'm not saying everyone's rig would benefit by changing. Maybe your rig boils good throughout the pan and you can't see a reason for moving anything. But there are many guys out there who are trying to figure out a way to increase the activity at the rear of their pan. This is one way of doing that and it worked very well for me.

The term "choking" is entirely incorrect terminology. I have not hindered my draft at all by doing this modification. I've only helped my flue pan extract as much heat as it can within the entire lengths of its flues.

Steve

[vtsnowedin]

Brent,

You would be surprised as to how much of a difference reducing the gap can make. Its not a "night and day" type of difference, but there is a difference. I now have boiling in areas of my flue pan that had no boiling before. That's a noticable difference in my opinion.

The opportunity for heat transfer is lost at the back when the heat and gases are allowed to exit the flues sooner than they need to. I'm not saying everyone's rig would benefit by changing. Maybe your rig boils good throughout the pan and you can't see a reason for moving anything. But there are many guys out there who are trying to figure out a way to increase the activity at the rear of their pan. This is one way of doing that and it worked very well for me.

The term "choking" is entirely incorrect terminology. I have not hindered my draft at all by doing this modification. I've only helped my flue pan extract as much heat as it can within the entire lengths of its flues.

Steve
Oh I'm all for experimenting and fine tuneing. I was just trying to get into the nuts and bolts of why they are set up the way they are. Hopefully in the next week or so I'll get to boil through a tank or two of sap and can fine tune both the blower and the gap under the flue pan. We will have to compare notes at season end. May it run long and be three percent.

[Brent]

I guess if you make sure the gap is at least equal to the stack area then it should be OK. You pix look like your front door is pretty airtight so I would think the blower could be cranked up to get the flow where you want it.

Do you blow under the grate or down into the fire ?

I have often toyed with the idea of putting something in under the pans to induce turbulence up into the flues.

[farmall h]

vtsnoweden, I'm not too familiar with all the towns below Bradford-Failee area. By chance are you located near West Failee-Thetford?

I redid the bricking in my arch this fall 'cause it seemed that it didn't boil as well as it did in the past. What happened was that over the years when we ran the brush through the flues alot of the sand was dragged out. Once we rooled off the pans we found a 2-3" gap. Added and leveled sand and shortened the gap to roughly 6" from the stack. Hopefully this will improve the boil in the rear pan. In the past the boil would splash out!

[vtsnowedin]

vtsnoweden, I'm not too familiar with all the towns below Bradford-Failee area. By chance are you located near West Failee-Thetford?

I redid the bricking in my arch this fall 'cause it seemed that it didn't boil as well as it did in the past. What happened was that over the years when we ran the brush through the flues alot of the sand was dragged out. Once we rooled off the pans we found a 2-3" gap. Added and leveled sand and shortened the gap to roughly 6" from the stack. Hopefully this will improve the boil in the rear pan. In the past the boil would splash out!

.
.

Chelsea is about twentytwo miles west of the Thetford exit on I -91. just follow VT113 to the end and your there. Note that 113 is not fit for a low slung car at this point but they are going to do some stimulus work on it next summer.
I may have to adjust the gap under my flue pan. I thought the pan gasket would compress more then it has and I may need to add sand to compensate. I've read through the old Leader directions and they call for leaving just 1/2" under the bottoms of the flues. If the way it is now doesn't work well I will close it up to that as a first trial.

[Bucket Head]

My blower is plumbed in under the grates. I don't have any over-fire air, although I'm thinking about adding it.

The natural draft arch's might not get away with as small of gap as the forced draft ones of equal size, but thats where the experimentation comes in. I would play around and see if you could get more turbulence. Nobody knows how their arch/pans will react until they give an idea a try.

Maple syrup making as a whole can be called the annual springtime experiment. I call it the ongoing science fair project. Were always trying to "tweak" some part of the process for better results.

Steve

[Amber Gold]

I adjusted the air gap yesterday and put the flue pan back on. I made the gap 8" from the stack collar. The base stack has about 10% additional area over the stack, and the 8" gives an additional 10% over that. I may test fire this weekend to see what I get for stack temps. I need to plumb the evap to the feed tank and clean pans first. I have an access hatch in the back and can adjust it from there if needed.

[Mac & Deb's Sugarhouse]

We've experimented for a few years as to how much of an air gap to leave and what to use on the deck of the arch. Our 2x8 raised works very good bricked to about 8 inches of the stack. We cover the brick with perilite insulation, and slope it down to the bottom of the deck, the bottom of the deck under the stack has one half bricks laid flat. We then take some ready mix concrete and sprinkle it over the perilite, spray it with water and let it harden. It keeps the perilite in place and also reflects heat, and lasts 3 to 4 years.

[Amber Gold]

I fired it up last night and got a much better boil than last year. Last year the sweet spot was 14-1600F and last night it was 1000-1200F. Also I had a better boil in more of the pan. I'm going to bring the ramp back even further to 6" from the collar and see if I can get it to 800-1000F...hopefully get an even better boil in the back of the flue pan.

[Amber Gold]

I made some more changes to my rear air gap. When I bricked the arch, I leveled the vermiculite off level with the arch rails and put the fiberglass type rail gasket on. Yesterday I measured the gap between the bottom of the flues and the vermiculite and it was about 1.5"...too much. I couldn't take my flue pan off to fix, so I installed a row of full brick which brought it up right to the bottom of the flues. I also moved the new row of bricks further back leaving a 3.5" gap from the brick to the back of the flues...not sure what this distance is relative to the flue collar as the pan was on and I didn't measure it. I also installed a partial row of bricks in the front ramp to bring that up to the bottom of the flues as well, I was one brick short to get it all the way across though...so between these two rows of bricks, there's the 1.5" gap from vermiculite to flue.

With these changes, my stack temps are now about 1100F and there is a noticeable difference in the boil in the back of the pan. I'd like to make some more changes, but now that I'm restricting the draft I'm getting ash, and sometimes flames, blowing out of the doors. I think with some more changes I can get stack temps down even lower and the boil even better, but I will need an air tight front to accomplish this.

Based on what I saw for a boil, I'd guess I'm in the 80 gph range. I'm taking tomorrow off and boiling. As of now, I have about 480 gal to process plus whatever comes in tomorrow.

Thanks for the info that is on this thread.

[vtsnowedin]

I sweetened the pans of my 3x8 Grimm lightening last night, the first real boil after moving it into a new sugarhouse and re bricking it. I too have about a 1 1/2" gap under the flues after the pan gasket. I boils pretty good as it is and I can fire it with the blower on full without getting fire in my face. I may push some sand up between the baffles to narrow the gap and dry stack another wall of bricks eight inches before the stack collar but if it makes it harder to fire or blows ashes out the doors I might switch back. I'll just have to try it and see. You'd have laughed if you'd seen me running around the first time the flue pan foamed up. I hadn't snipped the end on the new defoamer bottle and didn't have my jackknife in my pocket and it foamed right up and started drizzling down the outside of the pans. I had to open the doors and shut the fan off while I found a pair of pliers with a cutting notch in them. Of course there was a utility knife setting right there in the bucket of tapping tools but could I think of that. NOooo. Duh.

[Maplewalnut]

Josh- thanks for the update. I also narrowed my gap to the collar from 12in to probably 5 or 6 but still have no boil in the back of the pan. It rumbles almost out of the pan towards the front of my flue pan. My next thought is like you to reduce the gap to my flues. I may add another layer or cermaic blanket just to see. Right now my vermiculite is flush with the rails.

Mike

[Amber Gold]

Mike, unfortunately I made both changes at once, so I don't know if one or both changes made the difference.

With the difference in boil rate I'll deal with the ashes and occasional flame.

[red maples]

Is 1100 degrees the internal temp???

[Amber Gold]

Brad, those are internal stack temps. I think if those were external things would be near melting.
Going through my notes and the changes I've made. Changes haven't been for the better.

My original setup was the best. 60 gph on the first boil, but that was short and I burned my pan so I didn't run it as hard. The second boil was 73 gph. Every boil since has been around 55 gph. Tonight I'm going back to the original setup (8" gap from rear ramp to stack collar), but will leave the brick at the bottom of the flue. I fit a full brick in there so that's a 2.5" gap. This should keep the heat in the flues, but give it plenty of room to flow through the pan. If that still doesn't get me back, then I'll try a split brick. If that doesn't work then I'll go completely back to my original setup.

I'll keep everyone posted with my results. Hopefully I get a good setup this weekend. I have a lot of sap to boil.

[Justin Turco]

I have a raised flue pan. I have about 1" of space under the flues. I ran it like that all the way back to within about 6 inches of the metal base that the stack sits on. when you put the pan in place it closes up to about 4 inches. Ours boils pretty good.

PS. I pull all the fire brick out of this area at the end of the year vacuum it out and coat everything in there with oil to help keep it from rusting.

[JohnsSugarShack]

Had a chance to boil down 100gal last Monday and things went great except for the boil over on the flue pan, it happened fast but got the defoamer in quick and things calmed right down. I left about 10" open on the back and seemed to have a good solid boil 2/3 rds back in the pan, the back 3rd of the pan was still boiling pretty good just not as hard, very pleased for the first time. May close it up a little more next year but for now I'm going to leave it the way it is. The information on this forum is excellent and I thank every body for their help.:D

[johnallin]

Had a chance to boil down 100gal last Monday and things went great except for the boil over on the flue pan, it happened fast but got the defoamer in quick and things calmed right down. I left about 10" open on the back and seemed to have a good solid boil 2/3 rds back in the pan, the back 3rd of the pan was still boiling pretty good just not as hard, very pleased for the first time. May close it up a little more next year but for now I'm going to leave it the way it is. The information on this forum is excellent and I thank every body for their help.:D

John, I have only done a test boil with water on my patriot pans, any hints on how to avoid the boil over in the flue pan? I will be doing the "real thing" this weekend. How deep did you run the flue pan and how deep in the syrup pan.
You are right about how valuable this forum is - I agree whole heartedly.

Thanks and have a good weekend.

[vtsnowedin]

John, I have only done a test boil with water on my patriot pans, any hints on how to avoid the boil over in the flue pan? I will be doing the "real thing" this weekend. How deep did you run the flue pan and how deep in the syrup pan.
You are right about how valuable this forum is - I agree whole heartedly.

Thanks and have a good weekend.
From my recent experience :rolleyes: I would hint that you should not wait until it's foaming up to open the bottle of defoamer or to snip the tip off. As soon as you see any foam collecting in the flue pan add a drop of defoamer and then expect to add a drop halfway between each firing or so.

[johnallin]

Thanks, sounds like you did something I would do, everything in its place.......but where was the place I put it?

All kidding aside thanks for sharing that experience, I will be sure to snip the top off the defoamer- before I fire up!!

Now....how deep do I want to run that flue pan?

[JohnsSugarShack]

vtsnowedin, you are exactly right don't wait till the last minute. I had the bottle open but didn't think I needed the defoamer at the time. I'd recommend putting some defoamer in before it starts to foam up just another lesson learned. Figure I only lost about a quart of sap but I had to clean the sides of the flue pan. You know it's new and want it to look pretty. John I ran 2" above the flues and 1 1/2" in my syrup pan seemed to run good, haven't drawn any off yet but I will this weekend. I know I could probably run less in the front pan, just wanted to play it safe. Plan on boiling again on Sunday should have about 200 gal by then. Love this new evaporator, already talking about doubling taps next year and my wife just shakes her head. Got the bug.:D :lol:

[vtsnowedin]

Thanks, sounds like you did something I would do, everything in its place.......but where was the place I put it?

All kidding aside thanks for sharing that experience, I will be sure to snip the top off the defoamer- before I fire up!!

Now....how deep do I want to run that flue pan?
Oh there was no harm done just me looking silly running around the arch looking for something sharp while opening the arch doors and shutting off the blower and the smell of burnt sap where the sap ran down onto the arch rails and sides. Looked like a Chinese fire drill.
My rig like many older ones has a four foot pipe that carries the fresh sap from the float/preheater box to the front of the flue pan. It rests right on top of the raised flues so is level. I like to run rigs like that so that the pipe is just covered in sap (after you add the defoamer). You can see how the level is doing from six feet away just by looking at that pipe. That gives you about an inch and a quarter over the flues.

[johnallin]

vtsnowedin, Thanks. I ran today with just the top showing, but still had a flare up in the flue pan after only an hour of running. My set up is similar to yours with two pipes from the float box. You switch determine which side you want to run on by plugging one or the other.

Was pretty funny , son asked if this is normal, I say no! and we open the fire door, push down on the float to flood the pan all the while trying to remember where in the h^&* I put the defoamer. I did cut the top off before we fired, just could not remember where I placed it!

6 yr old grandson's eyes were as big as plates wondering why grandpa was running around in circles so fast...

All in all a good day, we boiled off 110 gallons between 1:15 and 5:30 and had fun.

[vtsnowedin]

Was pretty funny , son asked if this is normal, I say no! and we open the fire door, push down on the float to flood the pan all the while trying to remember where in the h^&* I put the defoamer. I did cut the top off before we fired, just could not remember where I placed it!

6 yr old grandson's eyes were as big as plates wondering why grandpa was running around in circles so fast...

All in all a good day, we boiled off 110 gallons between 1:15 and 5:30 and had fun.
It sounds like a great day to me. No grand kids here as yet put the powers that be are planning a wedding for this fall so soon enough. I did have a sugarhouse full of family this weekend helping out. Made nine gallons and the only loss was that the rope to the stack cover blew over and touched the stack and burned off. When I move the ladder around today to hitch it back up I think I'll splice in a section of wire to keep that from happening again.

[Amber Gold]

Latest change. ~1" air gap to the flues at the front and rear ramp...gap in between is still 1.75-2" as I can't get in there to pick that up w/out taking the pan off and can't do that by myself. Back ramp to stack collar is back to 8".

I got 60+ gph over the weekend...improvement over 55 gph. Raging boil the first half with 1300-1500F stack temps. Boils pretty good the back half. I think it should be raging the entire length with those stack temps so the heat's going someplace other than the pans so I'm not sure what the next step will be. Raise the front and rear ramps right to the flues or take the flue pan off and raise the gap between the flues to 1" of the flues.

I think 70-75+ gph should be attainable and will continue to tweek it until I get there.

[Haynes Forest Products]

Amber Gold sounds like you have a heck of a draw going thru the rig. How hard would it be to restrict the flue pipe to see if that helps with the high temps. Last year we just put a chunk of sheet metal on the top with a brick to hold it down:) blocked off about a 1/3rd

[vtsnowedin]

Latest change. ~1" air gap to the flues at the front and rear ramp...gap in between is still 1.75-2" as I can't get in there to pick that up w/out taking the pan off and can't do that by myself. Back ramp to stack collar is back to 8".

I got 60+ gph over the weekend...improvement over 55 gph. Raging boil the first half with 1300-1500F stack temps. Boils pretty good the back half. I think it should be raging the entire length with those stack temps so the heat's going someplace other than the pans so I'm not sure what the next step will be. Raise the front and rear ramps right to the flues or take the flue pan off and raise the gap between the flues to 1" of the flues.

I think 70-75+ gph should be attainable and will continue to tweek it until I get there.
I think your a little optimistic there. Checking old and new references I see that a 2.5x8 rig with a 5 ft. flue pan has about 90 feet of heated surface area. The exact number depending on who made it and the number,length and depth of the flues. That would give you 60 gallons per hour with traditional bricking and perhaps 65 with insulating arch board under the bricks to cut off that loss of energy. To get to 70-75 your talking air tight ,top air, preheater in steam hood etc. Or you can part with some of that moldy old money in your wallet and buy a steamaway from Leader and get up to 82 gallons per hour. Just $5306 for a 2.5x5. Remember it's only money. :rolleyes:
If your getting 60 per hour averaged over a eight or nine hour day counting start up and shut down your doing pretty darn good for the harness you got on.

[Amber Gold]

Haynes, I tried restricting the draft in when it exits the flue pan, but that just pushed the hot spot under the syrup pan, my stack temps did drop to 1100F though. I guess if I moved the restriction further up that it'd change that.

With all the changes I've made, wood consumption has not changed.

VT, Tuckermtn has the same rig, but bone stock and he averages 55 gph. I'd think with the blower a 30% increase should be attainable, so that's about 70 gph. If I went airtight with overfire air w/ preheater I should be in the 120 gph range. There was a topic on here last year and someone has an 802maple special that gets that at 2.5x8. Royalmaple has a 3x8 802maple special that cruises at 120 gph and can get 150 gph...I think he does air injection though so that's ~10% increase.

I agree it's a lot to ask out of an older style arch, but I think it's attainable. Based on what I could be getting for boiling rate in the back half of the flue pan, there's un-utilized potential. CDL's evaporator owner's manual claims 72 gph on a 2.5x8, but they're using an 11" stack (I think Leader's is 12")...I don't know the height of stack. I need a new base stack this year, so I wonder if I should drop stack size while I'm at it. I wonder if that's my real problem...the stack size is creating too much of a draft??

[Hop Kiln Road]

Josh - I'd like to come over and look at your rig...something doesn't seem quite right. Bruce

[vtsnowedin]

Haynes, I tried restricting the draft in when it exits the flue pan, but that just pushed the hot spot under the syrup pan, my stack temps did drop to 1100F though. I guess if I moved the restriction further up that it'd change that.

With all the changes I've made, wood consumption has not changed.

VT, Tuckermtn has the same rig, but bone stock and he averages 55 gph. I'd think with the blower a 30% increase should be attainable, so that's about 70 gph. If I went airtight with overfire air w/ preheater I should be in the 120 gph range. There was a topic on here last year and someone has an 802maple special that gets that at 2.5x8. Royalmaple has a 3x8 802maple special that cruises at 120 gph and can get 150 gph...I think he does air injection though so that's ~10% increase.

I agree it's a lot to ask out of an older style arch, but I think it's attainable. Based on what I could be getting for boiling rate in the back half of the flue pan, there's un-utilized potential. CDL's evaporator owner's manual claims 72 gph on a 2.5x8, but they're using an 11" stack (I think Leader's is 12")...I don't know the height of stack. I need a new base stack this year, so I wonder if I should drop stack size while I'm at it. I wonder if that's my real problem...the stack size is creating too much of a draft??

Well you already have a 14" stack which is the same size as my 3x8's so you probably have plenty of draft and running the blower might not give you more then a five or ten percent boost. The old rule was fifty sq. ft. of heating surface for a barrel of sap (32 gal.) per hour and that was without fans but it did assume good wood and an adequate stack both in diameter and height. If you push a given amount of air through a smaller pipe it will increase the velocity of the air in the stack but not in the wider less restricted area of the arch. You can as Haynes has suggested damper the stack you have and find out the optimum volume of air per hour for your rig. No point in whipping it past the flues so fast it doesn't have time to transfer its heat to the sap and also no point it letting it lollygag around after the sap has cooled it. If you were a graduate student I'd say that your conclusion is that "More research is needed" and you should apply for a grant form the stimulus fund.:lol:
Keep us posted and if you get to 70 or better without going air tight I'll be very interested in exactly how you did it.

[Amber Gold]

Bruce, you're welcome to stop in whenever you have time.

I am intrigued by Haynes's idea of putting a sheet of metal over the stack. I could knock it down to an equivalent 11" dia. stack area and see what it does. Although with the restriction being so high up and not the entire stack I"m not sure if that would have the same effect as having the entire stack be 11".

Keep in mind, that with all the changes I've made, I have not consumed more wood, but my stack temps and boil rate have changed. When I restricted the draft with the rear ramp, I think it restricted things too much and in the wrong location. I'm wondering if the restriction needs to be in the stack instead??

I think a friend is coming over tomorrow and we'll make some more mod's and should have enough to boil on Thursday.

What's the difference between CDL/Maple Pro's evaporator that claims 72 gph stock and my Grimm Lightning which is 55 gph stock?

If I can go from 60 gph to 70 gph, that's a 17% increase, which is a big reduction in my time.

[Maplewalnut]

Josh-

For comparison purposes, I have a 8 inch stack on my Algier 2X6 but have probably 25 feet of it. I think I have the same problem, too much draft. My back third of my flue pan doesn't even bubble.